Linear tricobalt compounds with di-(2-pyridyl)amide (dpa) ligands: Studiesof the paramagnetic compound Co-3(dpa)(4)Cl-2 in solution

Solutions of Co-3(dpa)(4)Cl-2, where dpa = di(2-pyridyl)amide ion, in CD2Cl 2 were studied by NMR in the temperature range 183-303 K. The spectra show only four H-1 and five C-13 resonance signals, consistent with the D-4 symm etry of the molecules found in the solid. The magnetic susceptibility in so lution was determined by the Evans method from 193 to 308 K. These observat ions can be modeled as an S = 1/2 to S = 5/2 spin-transition process with D elta H = 7.7(2) kJ mol(-1) and Delta S = 20.8(8) J K-1 mol(-1).